Color filter arrays are widely used with liquid crystal displays (LCDs) to provide color pixels. In such displays, each pixel is arranged to emit or reflect light through a color filter. The pixels are typically substantially rectangular with sides having lengths ranging from tens of microns to hundreds of microns, depending on the display size and resolution. For example, a pixel and corresponding color filter can have a size of 100 microns by 200 microns and a thickness of approximately a micron to tens of microns. A typical display can have a fill factor (the percentage of the display area covered by pixels and color filters) of 50% or even more.
The color filters are typically made using photolithographic processes in which surfaces are coated with a material (for example by evaporation, thermal transfer, or by a liquid coating containing dyes or pigments). The coated layer is then cured, if necessary, and photolithographically patterned, for example by coating a photoresist, exposing the resist to light such as ultra-violet (UV) light through a mask to develop a pattern in the resist corresponding to the mask, and etching the patterned resist and the underlying coated layer to form a color filter pattern corresponding to the mask. This process is expensive and time consuming because it is a subtractive process that is wasteful of etched materials, uses additional, expensive materials such as photoresists and masks, and requires expensive optical alignment equipment.
U.S. Pat. No. 6,497,981 describes a method of forming a color filter array. A substrate having a passivation layer thereon is provided. A negative color photoresist layer is formed over the passivation layer. A photolithographic exposure process is conducted using a light source with a wavelength less than or equal to 248 nm so that a pattern for forming a color filter array is imprinted on the negative color photoresist layer. In an alternative method, U.S. Patent Application Publication No. 20130038958 discloses a manufacturing method of a color filter array including providing a substrate; forming a light shielding layer on the substrate, the light shielding layer having a plurality of openings, the openings exposing a surface of the substrate, the light shielding layer having a height H; performing an inkjet printing process to inject color filter ink into the openings of the light shielding layer; and performing a solidifying process to solidify the color filter ink to form a plurality of color filter patterns. In yet another approach, EP0365219 teaches a method of making an array of a repeating mosaic pattern of colorants carried on a support using (a) a plurality of donor materials each comprising respectively a sublimable dye of a different color, and (b) a receiver element comprising a support having thereon a dye-receiving layer, wherein each donor material is in turn brought into face-to-face contact with the receiver and heated patternwise by contact with a heated embossed surface to transfer the desired pattern of dye to the dye-receiving layer.
It is also known to form small-scale features in thin layers of curable materials such as cross-linkable polymers using an embossing or imprinting process. In such processes, a curable layer is coated over a substrate, the curable layer is imprinted with a stamp having desired relief features that project from the stamp surface into the curable layer, the curable layer is cured using heat or radiation depending on the attributes of the cross-linkable polymer, and the stamp is removed. Such processes can be fast, cover large areas, and are applicable to inexpensive roll-to-roll manufacturing processes. However, the area that is imprinted with a relief pattern is typically much smaller than the area that is not imprinted, since the imprinting process displaces material that must flow to another location in the imprinted layer. Thus, the imprinted area is relatively small compared to the total area of the cured material and the size of the features in the relief pattern is likewise relatively small, for example less than 20 microns in width. Thus, imprinted structures over a substrate typically have a small fill factor.
Methods for filling imprinted features in a layer are known, for example coating curable material over an imprinted substrate with relief features, removing excess curable material from the surface of the imprinted substrate but not the imprinted relief features, and curing the curable material in the relief features. However, as with the imprinting process itself, it is difficult to uniformly fill a large, imprinted area with a liquid that is subsequently cured. For example, the coffee-ring effect is widely known to compromise the uniformity of a dried coating because of capillary flow induced by differential evaporation rates over the extent of the coating.
Therefore, because of such imprinting and drying problems, it is difficult to form large fill-factor substrates, such as color filter substrates, using imprint-and-fill processes.